Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$249.82	5.604%	$263.8199	$263.82	$263.80	$263.80
Purchase #2	$53.29	12.179%	$59.7802	$59.78	$59.80	$59.80
Purchase #3	$70.53	9.408%	$77.1655	$77.17	$77.15	$77.20
Purchase #4	$199.57	12.326%	$224.169	$224.17	$224.15	$224.20
Purchase #5	$83.78	11.703%	$93.5848	$93.58	$93.60	$93.60
Purchase #6	$221.33	12.642%	$249.3105	$249.31	$249.30	$249.30
Purchase #7	$104.83	7.584%	$112.7803	$112.78	$112.80	$112.80
7 purchase totals =	$983.15		$1,080.6102	$1,080.61	$1,080.60	$1,080.70